Question: The scale on a map is 5cm : 4km. If two cities are 40cm apart on the map, what is the actual distance in km between the two cities?
Explanation: The scale means that every 5cm on the map corresponds to an actual distance of 4km. A distance of 40cm on the map is the same as 8 $\cdot$ 5cm. The actual distance between the two cities is 8 $\cdot$ 4km, or 32km.